The present invention relates to a liquid crystal matrix display device such as used for a television display.
Liquid crystal televisions have recently been commercialized and the demand for them has rapidly increased. In general, NTSC-type television broadcasting is received by liquid crystal televisions, but in this type of broadcasting, 60 fields are transmitted per second and when the polarity of an image signal is reversed for each field in order to drive the liquid crystal with alternating current, the liquid crystal is subjected to a 30 Hz drive.
Generally, if a liquid crystal is not driven above 40 Hz, flickering is produced quite strikingly.
For this reason, an art for eliminating flickering has been proposed, which is disclosed in Japanese Patent Laid-Open No. 15338/1984. In this art, a single polarity image signal and a given potential of direct current are supplied to a picture element alternatively while switching them for each field. Consequently, an image signal to be supplied has a single polarity, and thus it is possible to restrain the production of flickering.
However, the above-mentioned art has a disadvantage in that shading irregularity occurs between the upper and lower portions of a picture. In other words, as regards to the picture elements in the upper portion of a picture, a signal is written on a source line immediately after switching to an image signal or direct current and the source line is then held in the signal switched state, and thus the amount of leakage of charges stored in the picture elements to the source line is relatively small and does not lead to any significant problem. As regards those in the lower portions of a picture, however, either an image signal or direct current is written on the source line at the end of a field scanning and the source line is thus switched to an image signal or direct current, and the potential of the charges stored in the picture element is therefore greatly different from that of the source line, and leakage of the charges results. Furthermore, since this leakage of the charges continues for a period of time which is substantially equivalent to one field, it is impossible to reproduce a true image in the lower portion of a picture, whereby shading unevenness is produced as between the upper and the lower portions of a picture.